The present invention relates to fluorescence polarization instruments of the type typically used to analyze body fluid samples treated with fluorescent materials and more particularly, to an improved electro-optical detection system for producing digitally compatible data signals indicative of fluorescence levels emitted from such samples for more effective computerized analysis thereof.
In the field of analytical chemistry, fluorescence polarization instruments are well known for their use in clinical applications. Particularly useful in medical laboratories, such instruments can rapidly analyze body fluid samples, such as those of a patient's blood, which have been treated with a fluorescent material in order to determine the presence and molar concentration of selected substances in the samples.
Generally, these fluorescent polarization instruments operate so as to direct one or more beams of linearly polarized excitation light upon the treated sample. The excitation light is typically of a high intensity and monochromatic corresponding to the peak of the absorption spectrum of the sample. The fluorescent molecules, when excited by the polarized light, emit luminous energy which, in its polarization value, decisively depends upon the molecular size of the species which fluoresces. The degeee of polarization also depends upon other parameters, such as, for example, the number of type of these molecules, the state of the molecules, i.e. whether or not the molecules are bound or unbound to one another.
The illuminated fluorescent sample therefore becomes a secondary source of radiation, emitting light in a spectrum peaked at a somewhat longer wavelength than the excitation light. A vertical polarizer in the emission light path passes vertically polarized light to a photosensor for detecting the resulting emission light from the sample and measuring the intensity of the fluorescent emission. A second polarizer in a separate emission light path passes horizontally polarized light from the radiating fluorescent sample to a second photosensor to simultaneously measure the horizontal component of a fluorescent emission and permit a complete and accurate determination of the degree of polarization of the emitted light.
In the detection and conversion circuitry, existing fluorescent polarization instruments have generally utilized photosensors, the current outputs of which have been amplified and converted to meaningful measurement signals using typical analog methods. The dynamic range and linearity, however, of these instruments has been limited due to inadequacies of the analog system in signal amplification and conversion. Furthermore, such analog conversion systems have been less than satisfactory in operating over a wide range of emission light intensities, particularly at lower intensity levels. While some designs heretofore developed for analog-to-digital conversion have increase accuracy and resolution of the fluorescence measurements, such designs have been expensive and somewhat difficult to produce.